It is well-known in the art that deionized water can be created by moving tap water through an ion exchange resin bed. In one method, resins fill much of a cylindrical tank. The resins can be of a mixed bed type. For the purposes of this invention, a “mixed bed resin” is a blend of a cationic and an anionic resin, in an equivalent ratio of 1:1.
In such systems and methods, water enters the top of the cylindrical tank, and moves downwardly through the resin within the tank. When the water has moved through the resin and reached the bottom of the tank, it has been deionized.
At this point, the deionized water flows into slots at the bottom of a hollow tube. The inside of the hollow tube contains no resin, but is typically surrounded by the resin within the tank. After entering the slots at the bottom of the tube, the deionized water moves upwardly through the hollow tube, and out of the tank.
High purity water can also be prepared by deionization through reverse osmosis. In high purity water systems, the ion exchange resin bed and reverse osmosis deionization technologies may be used either separately or together.
Many moderate to medium volume users of high purity water systems use ion exchange resin systems. Typically, two kinds of ion exchange resins are used for water deionization. The first kind of resin is a cationic resin, which removes cations from the water. The second kind of resin is an anionic resin, which removes anions from the water. These resins are eventually exhausted, lose their ability to deionize water, and thus need to be regenerated. These moderate to medium users of high purity water systems depend upon local service companies. In connection with such services, a tank with exhausted resin is replaced by a tank with fresh or regenerated resin. The service then regenerates the exhausted resin, using an acid such as hydrochloric acid or sulfuric acid for cationic resins, and caustic, such as sodium hydroxide, for the anionic resins. The regeneration process in such portable exchange systems takes place off site in a regeneration facility of the service provider.
There are many different versions of such prior art systems. As noted above, reverse osmosis systems may be used independently, and are viable alternatives for the preparation of high purity water. However, reverse osmosis systems are often higher in cost, require additional pretreatment and storage equipment, and typically rely upon a final, resin bed “polisher” tank to provide high purity water.
Resin-based systems are also common, and are typically used where higher capacities are required. A first such resin-based system has two tanks connected in series. The first tank contains a cationic resin, and the second tank contains an anionic resin. Under such an arrangement, both such tanks are typically exhausted simultaneously. The quality of water is determined by its specific resistance; the higher the specific resistance, the higher the quality of the water. Commonly, the two tanks are removed when the specific resistance of the deionized water has fallen to about 20,000 ohms-cm.
Another resin-based system has two tanks connected in series, and both of these tanks contain a mixture of an anionic and cationic resin, otherwise known as a “mixed-bed” resin. This type of system, using identical tanks, provides for a main deionization tank, followed by a so-called “polisher” tank. This type of system also provides for a back-up tank, in essence a second deionization tank, between the main tank and the polisher tank, to enable deionization to continue even in the event that the first tank fails or is exhausted. These types of systems are typically used where higher water purity qualities are required. The first tank is removed and replaced with a tank containing regenerated resin, when the specific resistance of the deionized water has fallen to about 200,000 ohms-cm.
A third type of resin-based system is a hybrid of the above two described resin systems. Particularly, this third system includes one tank having a cationic resin, a second tank having an anionic resin, and a third tank having a mixed bed resin. The first two tanks are the so-called “worker” tanks, while the third tank is the “polisher” tank, to achieve high levels of water purity.
The flow pattern in each of these prior art systems is like the prior art system shown in FIG. 2, i.e., the “down-flow” type, where the unpurified water enters the tank and moves downwardly through the resin for deionization.